Dasuquin!
It’s a glucosamine and chondroitin supplement with avocado/soybean unsaponifiables. It’s joint support just like any human with arthritis should be on, but specially made for kitties.
We have a 13 year old overweight cat with arthritis, chronic renal failure AND a plate in her leg and we give her Dasuquin in the morning sprinkled on her wet food. She’s been on it for about 9 months and it’s really working wonders. She hops right up the stairs and even jumps on the counter tops. You should definitely ask your veterinarian about it.
As for pain management now (until the glucosamine starts kicking in), you can talk to your vet about that. Metacam is a great NSAID that is often used off-label for cats and you can even get as serious as buprenorphrine, a controlled substance, that is more potent than morphine.

I have been giving my 19 year old cat Syn Flex. A year ago she came down with arthritis so bad I thought she would have to be put down. Now she actually runs around and plays. It takes a little while to start working and you have to give it every day but it really does work.
Another herbal product I gave my cat was called “Dog gone pain” For cats and dogs. It works faster and you can use it until the Syn flex starts to work.

I’m with convert to metric. My cat was diagnosed with arthritis at age 15. My vet put him on Metacam as a means of quickly relieving the inflammation and making him more comfortable, but he doesn’t recommend using it long term. It’s an NSAID, similar (but not identical) to Ibuprofen. Given the nature of the drug, cats can have the same long-term issues from its use that we can from long-term use of Ibuprofen. At the same time he started the Metacam, he also had me give him Dasuquin. After two weeks, there had been enough time for the Dasuquin to begin making a difference and he was taken off the Metacam. I did a few other things to help him as well. I added pet steps to his favorite areas that were higher, such as the bed, to reduce some of the stress on his joints. I put a heating pad in his favorite sleeping spot and kept it turned on low, and also massaged his muscles and joints daily. All of these things combined seemed to make a huge difference in his quality of life. He lived happily to the age of 18. I do, however, recommend that you discuss any therapy with your vet before beginning it.